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36
Intel
82865G/82865GV GMCH Datasheet
Signal Description
2.5.5
PCI Signals–AGP Semantics
PCI signals are redefined when used in AGP transactions carried using AGP protocol extension.
For transactions on the AGP interface carried using the PCI protocol, these signals completely
preserve PCI 2.1 semantics. The exact roles of all PCI signals during AGP transactions are defined
in the following table.
Signal Name
Type
Description
GFRAME#
(2.0)
GFRAME
(3.0)
I/O
s/t/s
AGP
GFRAME(#):
This signal is driven by the current master to indicate the
beginning and duration of a standard PCI protocol (“frame based”) transaction
and during fast writes. It is not used, and must be inactive during AGP
transactions.
GIRDY#
(2.0)
GIRDY
(3.0)
I/O
s/t/s
AGP
GIRDY(#):
This signal is used for both GFRAME(#) based and AGP
transactions. During AGP transactions, it indicates the AGP compliant master
is ready to provide
all
write data for the current transaction. Once GIRDY(#) is
asserted for a write operation, the master is not allowed to insert wait states.
The assertion of GIRDY(#) for reads indicates that the master is ready to
transfer to a subsequent block (4 clocks) of read data. The master is
never
allowed to insert a wait state during the initial data transfer (first 4 clocks) of a
read transaction. However, it may insert wait states after each 4 clock block is
transferred.
NOTE:
There is no GFRAME(#) – GIRDY(#) relationship for AGP
transactions.
GTRDY#
(2.0)
GTRDY
(3.0)
I/O
s/t/s
AGP
GTRDY(#):
This signal is used for both GFRAME(#) based and AGP
transactions. During AGP transactions, it indicates the AGP compliant target is
ready to provide read data for the entire transaction (when the transfer size is
less than or equal to 4 clocks) or is ready to transfer the initial or subsequent
block (4 clocks) of data when the transfer size is greater than 4 clocks. The
target is allowed to insert wait states after each block (4 clocks) is transferred
on both read and write transactions.
GSTOP#
(2.0)
GSTOP
(3.0)
I/O
s/t/s
AGP
GSTOP(#):
This signal is used during GFRAME(#) based transactions by the
target to request that the master stop the current transaction. GSTOP(#) is Not
used during AGP transactions.
GDEVSEL#
(2.0)
GDEVSEL
(3.0)
I/O
s/t/s
AGP
Device Select:
During GFRAME(#) based accesses, GDEVSEL(#) is driven
active by the target to indicate that it is responding to the access.
GDEVSEL(#) is Not used during AGP transactions.
GREQ#
(2.0)
GREQ
(3.0)
I
AGP
Request:
This signal is an output of an AGP device. Used to request access
to the bus to initiate a PCI (GFRAME(#)) or AGP(GPIPE(#)) request. GREQ(#)
is Not required to initiate an AGP request via SBA.
GGNT#
(2.0)
GGNT
(3.0)
O
AGP
Grant:
This signal is an output of the GMCH, either granting the bus to the
AGP device to initiate a GFRAME(#) or GPIPE(#) access (in response to
GREQ(#) active) or to indicate that data is to be transferred for a previously
enqueued AGP transaction. GST[2:0] indicates the purpose of the grant.
GAD[31:0]
(2.0)
GAD[31:0]
(3.0)
I/O
AGP
Address/Data:
GAD[31:0] provide the address for GFRAME(#) and GPIPE(#)
transactions and the data for all transactions. These signals operate at a 1X
data rate for GFRAME(#) based cycles, and operate at the specified channel
rate (1X, 4X, or 8X) for AGP data phases and fast write data phases.